Detective Twilight Sparkle must pursue the most brilliant killer she ever confronted - a mysterious criminal called the Masterhorse!

In a series of crimes that have stunned canterlot, bank robbers have been killing bank employees and there family's if the robbers instructions are not followed to the letter. Twilight Sparkle knows this is no ordinary criminal- the pathological need for control and perfection is too great. Sparkle is in the midst of a crisis at home- but the case becomes all-consuming as she learns that the masterhorse is planning one huge, last perfect crime....